Is this a ulcer?

On the rare occasion my goldfish gets a spot on his head in the same place but at random times I think he has had it come and go approx 4 times over the 6 years I've had him.
Can anyone identify what this may be? Is it just an injury? Ulcer? It clears everytime in two days but not sure if this is something more?
Photo attached

 

is there a chance you could get a clearer picture? and what do you use to treat it?

 

Tried to but this was the best pic I could get rest were blurry will see if its still there tomorrow.. To be honest it tends to just clear up on its own he had a water change today anyway so that may help but water conditions are all good at the moment I've tried melafix before and it's cleared up slightly quicker as I say it never lasts long but I'm wondering what it could be
Have zoomed in not sure if that helps its like one slightly raised red bump with a white head in the middle almost like a zit?

 

its healed now so I cant get another picture but he gets this from time to time and it just seems to clear by itself just wondering if its something I can prevent or if its an injury or a tumour not to sure but at the moment hes back to being healed rather strange

 

It looks like the fish, due to the naturally poor eyesight, is swimming into something...frequently. Have you got anything hard, narrow and vertical in the aquarium that it might have swum into?

Even something as innocent as a plant stem or an edge on an ornament would do that if repeated often enough.